The popularity and savagery of dog fighting was highlighted in the US yesterday when proceedings against one of the biggest stars in American football, Michael Vick, and three others began in a Virginia court.

The charges relate to a six-year dog fighting competition, known as Bad Newz Kennels, alleged to have been operating from Vick's 15-acre property in Virginia.

Dogs were alleged to have been subjected to cruelty beyond the fighting: they were apparently electrocuted, hung, shot or drowned.

Dogfighting, which was once mainly restricted to the rural south, has spread in recent years to the north and is a multi-million gambling business.

Meets are organised months in advance. Dogs run on treadmills to build endurance, and are often tormented to make them more vicious, particularly in the days before a fight.

All four men had entered not-guilty pleas when they appeared in Richmond, Virginia. But two of the accused - Purnell Peace, 35, of Virginia Beach, also known as P-Funk, and Quanis Phillips, 28, of Atlanta - yesterday pleaded guilty.

Another, Tony Taylor, pleaded guilty a fortnight ago. The three could give evidence against Vick in return for a lighter sentence.

Yesterday was the deadline for Vick to accept a plea deal or face more serious charges on Monday that could mean five years in jail. If he accepts the plea deal, he could face a year or more in jail. He was under pressure to accept the deal because of the prospect of the other three testifying against him.

Vick, who plays for the Atlanta Falcons, rose from a poor background to become one of the highest-paid stars in American football and, until the dog fighting scandal, was promoted as a role model for disadvantaged youth.

Although he has not been found guilty of anything the National Football League ordered him not to report for training until the case was resolved.

He could be penalised by the NFL for breaching its rules on good conduct. A player can be banned for life for illegal gambling or associating with gamblers.

Dog fights attract big money, compared with earlier years when they tended to be chaotic impromptu affairs involving small amounts of cash. Well-organised fights now have stakes starting at $25,000 (£12,500).

John Goodwin, a spokesman for the Humane Society of the United States, who specialises in combating such fights, said: "There is an organised world of dog fighting, bound by a dozen magazines and hundreds of websites."

Tio Hardiman, founder of the Chicago Campaign to Stop Animal Fighting, told Newsday that in preparing the dogs some of their handlers used a variety of tactics to torment them, including feeding them "dead bumblebees, so the stingers get caught in the gums, and they won't give them any water".

He said: "These dogs are deprived of light, water, food and human contact, so the dog knows the only way he's going to get anything out of his master is to display that grit."

Their trainers "don't have any feelings", Mr Hardiman said. "You have to be a Roman soldier to train a fighting dog. There are no excuses."

Family pets are often stolen as bait for the dogs. In some cases fighting dogs without the acceptable killing instincts have their muzzles wrapped with duct tape and are used as bait for more aggressive dogs.

Hanging injured dogs to allow other fighting dogs to tear them to pieces is also a popular training practice.